i'm agreeing with Rocco16. really looks like the heads are the choke point...

300rwhp is nothing to sneeze at, man...

 

My friends has same basic set-up, less head work, in his 97 LT1 Z28 and put down 302rwhp. Like other have said, I don't really think the head worked helped, there is a lot to porting heads. Also you don't want a mirror finish, it might look nice, but it hurts the laminar flow flow of the heads. The air now wants to "stick" to the walls since they are so smooth, it kills the boundary layer.

 

Whoa, hold on right there, if you "polished" the intake runners you've just made a HUGE mistake. You'll now have the gas "puddling" in the curved areas of the runners...simply put, the gas will not stay suspended in the air. Did you take pictures of the heads when you were finished by chance? Porting heads is a science, not to be taken lightly. Exhaust ports can, and should be polished to a degree, but not intake ports.

 

My 350 LT1 had essentially the same mods, but with stock heads, and I made nearly 346hp/352tq, on a Mustang dyno even. I'd say something is wrong.

 

I see now.....
Something about his combo is messing him up...but (again) not as much as he thinks.
I'm thinking he is only down about 20hp....? A tired motor could cost that much....

Larry
code5coupe

 

Zix,
There are some pics of the heads in the link below' about halfway through the post.
We had this discussion a long time ago about polishing the intake ports on the heads. At the time we discussed it the heads were already polished and installed on the engine. Your advice from a while back may we be good advice and this may be something that is hurting my performance.

Thanks for you comments.

prattman
http://forums.corvetteforum.com/show...post1555429950

 

rocco16,

My original post says, I was expecting 320 rwhp or more.
I don't think I am trying to make out as though I should have really high HP numbers as this engine project was a lot of compromises. It is my daily driver so I wanted good manners and driveability so I knew I would not be producing high HP numbers.
It is the missing 20 HP I am tring to find.
Thanks for your comments, I respect the opinions of everyone on the forum.

prattman

prattman[/QUOTE

 

Yes, see below.

Biography:
GM Hotcam
Cloyes double roller iming gear set
1.6 Crane Gold Race roller rockers
EM long tube headers (ceramic coated inside and out)
CSR electric water pump
Stock LT1 aluminum heads ported & polished
Comp Cams (26915) Beehive valve springs/retainers
Cut-back valves and 3 angle valve job (stock valves)
ATI SFI rated balancer
MSD Superconductor plug wires (red)
Upgraded to 95 timinig cover and vented optispark
EGR deleted
Air Injection deleted
NGK Iridium Spark Plugs
Cats Eliminated

 

When it’s all said and done you have a hot cam with 1.6 rockers, long tube headers and electric water pump as performance mods. Polishing of the intake ports could have hurt ya more than it helped ya. The water pump only makes gains at higher rpm and it’s not a lot.

I’d make a guess anywhere from 310 rwhp to 320 rwhp as the heads are a matter subject to some objective testing on a flow bench to see if you got anything out of them.

The best thing is post the entire dyno sheet so everyone has a little more to look at and scan the engine to make sure your not having some other problems. If you haven’t replaced the 02 sensors in a while I’d strongly suggest you do so as it’s amazing how much better a car runs with fresh 02 sensors. Always use stock 02's and not some aftermarket replacement. The GM computer is programmed to see GM 02sensors and they always work the best.

Also check your MAF to see if oil from something like a K+N filter is on the wires. That can throw off your fuel/air and kill power.

Not a fan of mail order tunes either. I’ve seen some dead on the money and others out in left field.

You may not be all that far off and a matter of just correcting a couple of minor issues. Most people fall short of their cars potential just because it not in perfect state of operation. The car needs to be 100% to be 100%.

 

Well, I'd be willing to place money on the heads costing you some serious power at this point, as well as even contributing to the "lean" condition you're seeing. I'd be interested to see if you have an erratic lean condition as well. While you did a nice job of polishing the ports, as stated eariler this actually hurts the air/fuel mixture as it heads into the chamber. The rough edges of the ports, in simple terms, creates a cusion of air by causing the air to "tumble" which keeps the vast majority of the air fuel mixture off of the intake port walls, and this helps to keep the fuel suspended in the air...a polished wall will not have this slight tumbling effect and the fuel instead will start to condense, for lack of a better word, on the intake port walls.

Here is a picture of my heads after they were ported by the same guy that ports Winston cup heads for factory Chevy teams (my heads are on top, factory LT4 heas are on the bottom);



You can see the slight, even roughness to the intake ports.

The exhaust ports can be, and should be polished though, that's perfectly fine. As much as this sucks to hear if I was in your posistion I would take the heads off and carefully rough up the intake ports to remove the polished finish.

EDIT; Holy crap my spelling sucks...long day

 

Hate to re-hash but...

This guy is some kind of head guru at some school. No bashing me please because I don't keep up on who's who in the performance engine game.

I'm glad I read all of this before I did my my heads, I was going to make the same mistake. You'd think a polished port would certainly help flow, it might but it doesn't work for the intake for reasons mentioned by Zix.

These are prattman's intake ports...

 

Wow! Those are some good numbers. I have basically the same mods with ported heads and was expecting numbers like yours. I ended up with 322 rwhp (on a DynoJet). The car is running better and will have it re-tested this winter. I still think that he is missing a good 20+ hp.

 

slow down guys...

mirror finish is not hurting him here at all... I always mirror finish intake ports on manifolds and heads and have some of the highest power numbers for the cams used on production LT1/4 cylinder heads, so that is a complete falsified myth for fuel injected motors where the injector has atomized the majority of the fuel while spraying under pressure. (if it were true direct injected engines would suffer from no atomization due to the injectors firing into the chamber directly on the compression stroke never seeing a port. it is a TRUTH for carbed motors where fuel comes out in droplets from the venturis and rely on turbulance in the following intake track to atomize the droplets by the time they reach the combustion chamber for a more uniformed mixture. I have been porting LT1/4 cylinder heads for a decade now with absolute disgust for the claims made by CNC ported heads stating that they create a "cushion of air" what they are doing in all actuality as seen by using smoked air is making a smaller port by increasing turbulance and making the runner smaller in terms of flow path. even at a mirror finish there is going to be some turbulance but much closer to the port wall which does not disrupt the flow characteristic of the port nearly as much as a rough finish or a CNC machine tool path. if the ribbed or rough finish were such a benefit to reducing resistance of airflow, jets would utilize this technology.. when is the last time you saw a rough finished jet fusalage? or cars which are designed to reduce wind resistance for top speed? the claims made were to reel in buyers and give them a warm fuzzy feeling while the truth of the matter is that the companies using CNC machines would have to invest more time per head to reduce the tool path ridges or make closer passes with the cutting bit. both of which require more time, more finite programming and in the end will reduce production and increase cost hurting the bottom line.

if you want to argue this point you are more then welcome, but if you would like to pull out dyno graphs and compare power made with several different cams... you better have some really impressive data.

an example of some of the port finishes used on prodcution untouched shortblocks with hot cams, GTP6 cam, 847 cam, 219 lingenfelter cam.. were all well well above the average seen by many on here. to date I know of one person using the hot cam that was able to beat out the numbers made with the hot cam and that was done using a 1.7 ratio rocker arm which took advantage of the flow at higher lift. pictures will be below.

on to the car in question.. something is off.. a bone stock hot cammed LT1 with nothing else done would be above 300rwhp even with stock manifolds and cats. if the dyno oerator shut the run down before it was through making power, it would make some difference, but not 30rwhp over 5-600 RPM in the end. the ports in the pictures don't look bad and would not contribute to the end result being as poor as it is. soemone nailed it in my opinion.. check for being a tooth off with the timing set. if it is an adjustable timing set check to make sure the crank sprocket is NOT on an advanced or retarded keyway, the hot cam has 4 degrees of advance preground into it and should be installed straight up with zero change of the base keyway location for maximum all around performance. also check to make sure your install height on the springs is correct, it should be fine considering the springs you are using, but checking never hurt. rocker arm adjustment.. if you used the spin method your rocker arms are way overtight. adjustment from zero lash is in terms of vertical movement the second they do not move up and down between the lifter and rocker arm is zero lash.. tighten 1/4 turn past this and lock the allen screw down.

make sure your fuel filter is clean and flowing well, make sure pump is not tired, make sure injectors are CLEAN or replace old and tired injectors. make sure your not seeing knock retard from noisy valve train and if you are and your timing is retarding excessively this will severely hurt performance. if the engine was rebuilt.. what is the calculated static compression ratio of the engine with the heads used? was a compression and leak down test performed to ensure the machine work was done correctly and there is not excessive piston to cylinder wall clearance or excessive ring end gap? is there crank case pressure at WOT? can you post the dyno graph with Air Fuel Ratio for us to review. did you get a log of the ECM while running the dyno pulls? go into as much detail of the build as possible to help us track down possible causes for the low numbers your experiencing.

Chris

 

Did you also check to see if you're actually @ WOT?

I've seen that happen on Dynos many times.

 

Actually I thought the rough finish was for the fuel to atomize better. Even though the injector is supposed to do that.

 

lcvette,

I couldn't have said it better, thank you.
I have been of the opinion that mirror polishing the intake ports HAS to produce better flow. As your aircraft surfaces analogy illustrates.
I spent many many hours polishing the intakes, and if I didn't think it would help, I would not have done it.
So far you and I are the only two that think the same way on this subject.

went to the 1/8th mile strip last night, only got two runs in before it rained. Both of the runs were bad 9.7 sec best, but it was me and not the car.
I was on street tires and spun alot, and my reaction times and 0-60ft are pretty bad. This is not a suprise as it was the first time I ever ran on a drag strip. Was a lot of fun and I will work on technique this summer.
I will get busy and post the dyno/air fuel stuf in a few minutes, i have been away from home all day.
I will get busy with checking fuel pressure, and I am not sure how to check the cam install, I will need to think about that.

To all that have responded, thanks, I do alue everyone's opinion, and I will get some more nfo up on this thread.

Thanks,
prattman
Oh, I lost the race by.9 sec. It was me and not the car.

 

Here ia a link to the dyno chart with air/fuel info. The line on top is HP and the lower is the air/fuel.
http://i58.photobucket.com/albums/g2...s/Dynopull.jpg

I also have a TTS datamaster scan I can email to anyone that woud like to see what else is happening.

Oh, the O2 sensors are new, and they are GM parts

 

If your scans turn out ok, please consider what I said about the cam being off 1 tooth. There is another forum member and I believe he went by Glock LT4, but anyways I believe it was he who had the same problem. He installed the hotcam a tooth off and didnt realize it. Finally figured it out when trying to dyno tune and was adding rediclous amounts of timing and just couldnt make any power. But trying to recall from memory, his did not run bad, it was just down on power. Good luck and let us know how it goes.

 

[QUOTE=lcvette]slow down guys...

.....go into as much detail of the build as possible to help us track down possible causes for the low numbers your experiencing.

Chris

QUOTE]

Chris,
It is a 94 LT1 4 bolt main out of another 94 vette.
I checked all of the specs per the FSM, and had the machine shop bore gage the cylinders. They recommended hone and new standard size cast rings which is what I did. Ring gaps were checked/installed per instructions provided and the FSM.
Main and rod journals were within specs per FSM, so I installed new standard size bearings and new cam bearings. New Cloyes bouble roller timing set and did the opti conversion to the 95 cover and vented opti.
Bottom end is stock, top end got the Hot Cam.
I posted all of this a long time ago and I could dig the links to them up if needed.

prattman

 

As soon s I can figure out th best way to check it I will. Do you have any suggestions?

Thanks,
prattman